The matrix type display device of the prior art stores graphic data, as inputted from image writing means such as CPU, temporarily in a built-in frame memory when the graphic data are to be displayed in a predetermined display panel.
Here, when the graphic data are read from the frame memory and outputted to the display panel, graphic data inputted from the outside may be overwritten midway of one frame thereof. Then, there may occur an event, in which the contents of the image of upper and lower portions of one frame are shifted with time, when the motion images or still images are displayed.
In order to prevent that shift of the image contents, in the frame memory, as conventionally described in the following Patent Publications, a write wait signal is outputted from the side of the matrix type display device to the side of the external image writing means, and the input of the graphic data to the matrix type display device is delayed until the end of reading the each frame of the graphic data. Thus, the write of the image in the frame memory is brought into the stop state thereby to control the synchronization properly between the write and read of the graphic data, so that the graphic data inputted from the outside may not be overwritten midway of the graphic data of one frame outputted to the display panel:
JP-A-2002-108268;
JP-A-2002-108316; and
JP-A-2002-202881.
As a result, when the motion images or the still images are displayed, it is possible to prevent the event, in which the image contents of the upper and lower portions in one frame are shifted with time, and accordingly to display a smooth image.